Zinc coated article



March 21, 1933. s, H DAVIS Er AL 1,902,621

ZINC COATED ARTICLE i Filed Nov. 2, 1928 Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE SIDNEY H. DAVIS AND' CARL 0. ANDERSON,

OF BAXTER SPRINGS, KANSAS, WILLIAM N.

SMITH, OF PLATTEVILLE, WISCONSIN, AND HERBERT R. HANLEY, F ROLLA,

MISSOURI, ASSIGNORS T0 THE CENTURY ZINC COMPANY, A CORPORATION OF OHIO ZINC COATED ARTICLE Application led November lhe principal object of our invention is to provide a zinc coated ferrous article capable of materially greater' resistance to corrcsion in the presence of weak acids than similar ferrous articles coatedxwith zinc b v methods heretofore generally commercially practised, namely, the hot dipping method or electroplating in alkaline soluixo tions of cyanide of zinc or in neutral or substantially neutral solutions of zinc sulfate by means of a current of relatively low density delivered from a soluble zinc anode to tlic article acting as a cathode, or in fact l? by any other method with which We are familiar.

Other objects, advantages, novel features and characteristics comprehended by our invention are hereinafter more specifically f T' mentioned or Will be aparcnt to those skilled in the art as a more detailed understanding of the invention is acquired from the following description.

Our 'invention contemplates the production of the zinc coating or plating on the ferrous article by electrolysis of solutions of zinc sulfate relatively high in acid by means of currents of high density delivered from anodes insoluble in said solutions, for

n example, in accordance With the method disclosed and claimed in an application for Letters Patent of the United States filed by us September 12, 1928 under Serial No. 305,-

429. As a result of the practice of that method We are enabled to produce a Zinc plated ferrous article exhibiting, among other things, improved resistance to corrosion in thc presence of Weak acids. While the said article has materially greater corrosionresistant properties than ferrous zinc plated articles of generally like character theretoforc produced commercially, the zinc coated ferrous article forming the `subject of the present application exhibits still greater corrosion resistant properties.

In the practice of the aforesaid method the surface of the ferrous article to be plated is thoroughly freed from foreign substances and scale so as to present a clean surface for the reception of the zinc and the latter 2, 192s. serial No. 316,875.

then plated directly thereon by electrolysis of a high acid solution of zinc sulfate. In accordance With the present invention, however, during and as apart of the operati-ons incident to rendering the ferrous article zinc-receptive, an eXtrem-ely thin coating of lead in one form or another is formed upon the article in such manner that what may be for convenience termed a leady-ferrous surface, as distinguished from a clean steel or iron surface is formed for the reception of the zinc. The surface-to which we have reference, and as Will hereinafter more fully appear, is of a character distinct from` a continuous,l permanent plating or coating of lead entirely covering the ferrous base and which would thus in itself form a base for the reception of the zinc when subsequently applied, substantially as the coating of copper which is frequently applied to brass or other non-ferrous articles prior to a coating of nickel forms of itself a base for the latter; in accordance with our invention, however, the initial or incipient lead coating does not of itself form a base and thus a distinct interposed layer or stratum'between the ferrous article and the plating of zinc but rather a component part of the ferrous base itself, intimately associated with the molecular structure thereof and thus forming therewith a compound leady-ferrous surface for the reception of the zinc.

The incipient thin coating of lead is desirably formed on the ferrous articles after the latter have been freed from foreign substances such as grease and scale in'any suitable Way and the formation and subsequent treatment of the coating may thus in one sense be considered as incident to and a part of the series of steps or operation designed to render the article zinc-receptive. Moreover, the said incipient coating of lead may be formed in various Ways aslwill hereafter more fully appear, but irrespective of the particular method employed to form it, the coating is subsequently subjected to a vigorous brushing or bufng, desirably with a steel Wire brush or like implement, so as to force a portion of the coating into the pores of the surface of the article and remove the excess of the coating and' thereby properly condition the article for the reception of the zine which may be applied thereafter by electrolysis of high acid solutions of zinc sulfate by means of currents of high density delivered from anodes insoluble in such solutions and preferably in accordance with the methods disclosed and claimed in our said application for United States Letters Patent Serial No. 305,429.

Reference Will now be made by way of example only and not in any limiting or restrictive senseto certain 'methods of producing the zinc coated article forming the subject 'of the present invention, but We do not thereby desire or intend to restrict ourselves specifically to the production of said article thereby as, if desired, the article may beproduced by any other suitable method.

.Ewa/mp3@ 1.-' l`heferrous article to be plated, for example, a steel sheet, is first inimersed in an alkaline solution, such as a Weak solution of caustic soda, to effect removal of any grease Whlch may be present .on the article and is then withdrawn from the -solution and thoroughly Washed. The article is then pickled for a suitabley length of time in an acid solution, such as a rela' tion.

The'article is next immersed in an alkaline bath preferably containing caustic soda and sodium carbonate, about 15 grams of the former and of the latter being desirably employed for each liter of solution, and a direct current then passed through this bath to the article acting as a cathode from an anode formed of some material insoluble or substantially sov in the bath under the conditions indicated;'an anode or anodes of iron may therefore be advantageously employed as they are cheap, readily manufactured .and practically insoluble in the bath in the presence of the electric current which is v preferably of relatively low density as, for

example', 30 amperes per sq, ft. of cathode surface, though currents of other density may be utilized if desired.

In addition to the alkaline ingredients a. suitable quantity of lead either in the metallic lstate or as lead oxide, lead carbonate or other suitable lead compound is introduced into the bath to provide the lead article.

for forming the coating on lthe ferrous For this purpose We prefer to utilize scrap metallic lead as the same is readily obtainable and can be readily introduced into the bath in the form of small blocks or pieces; a certain amount of this metallic lead :dissolves in the bath and forms sodium plumbate or some generally similar compound. As the quantity of lead required in the solution is relativelysmall, under certain circumstances it may be deemed preferable to utilize leadtanks for the bath and thereby obtain all or a portion of the requisite amount 'of lead through the action of the solution on the tank itself. However, as under these conditions the tank itself is gradually eaten away and thus ultimately rendered useless, it is ordinarily preferable to use iron or otherA tanks unaffected' by the alkaline solutionand to supply the lead from time to time as may be required either as metallic lead or in some other form at least slightly solublein the solution under the conditions present. While as stated, but a relatively small amount of lead is required in the solution, under ordinary conditions the greater the quantity thereof the less will be the time required to form the requisite coating on the article with a current of given density; thus the quantity of lead supplied to the bath Will be generally determined by the particular operating conditions encountered but in any case it is desirable that enough lea-d in metallic or other form be always present in the tank to insure a sufficient amount thereof in the solution or bath to enable the production of the requisite coating Within a reasonable time with the current Which is being employed, such as in from two to ten minutes when using a current of 30 amperes density per sq. ft. of cathode surface.

The lead coating produced upon the ferrous article under the conditions described is blackl or substantially black in color and of a distinctly spongy texture and thus presents distinctly different physical characteristics from metallic lead.

The electrolysis of the bath having been continued until the surface of the ferrous article is thoroughly coated with the spongy lead deposit, the article is then removed from the bath and Washed, and the coated surface of the article then very thoroughly brushed or bufl'ed with a steel Wire brush or like implement so as to cause a portion of the spongy lead coating to penetrate into the pores of the surface ofthe article and .mechanically unite therewith and also to plied to the article or the latter may be immersed in water to prevent oxidation until it be desired to apply the zinc. As hitherto stated the application of this metal in accordance with our invention is effected by electrolysis by currents of high density of high acid solutions of zinc sulfate utilizing the article as a cathode and an anode insoluble in such solutions, for example, anodes of lead, the method employed being preferably that disclosed in our said application Serial No. 305,429 and which briefly comprises the steps of forminga thin strike coating of zinc upon the article by electrolysis of an acid solution of zinc sulfate by a current of high density delivered from an insoluble anode to the article acting as a cathode, then removing the article from that bath and continuing the plating thereof with zinc by electrolysis of another bath comprising a solution of zinc sulfate of higher acidity than the first bath by a cur,- rent of relatively lower Vdensity than that previously employed, said current being delivered from anodes insoluble in the bath to the article acting as a cathode, until a plating of the desired thickness is attained to thereby produce a finished article of commerce.

Ewample 2.--Instead of forming the spongy lead coating upon the ferrous article by electrolysis of an alkaline lead-containing solution as in Example l, the coating may be formed, after freeing the article from grease and removing the scale by pickling and brushing as described in that example, by simply immersing the article in a solution of lead acetate or of lead chloride for a suitable period. Under these conditions the formation of the coating is slow when the bath is cold but becomes more rapid as the ,temperature of the bath is raised, and vthe spongy lead coating formed in this manner exhibits substantially the same characteristics as to coler and texture as that formed inthe manner here-l tofore described, but since its formation even in a warm solution is 'slow and a considerable time is thus required to produce a coating of the requisite thickness, the electrolytic method of forming the coating to which We have hitherto referred Will ordinarily be preferred.

After a coating of the requisite thickness has been obtained, the article is removed from the bath and subjected to the same treatment including Washing, brushing and plating with zinc, as described in Example 1.

Eample 3.-The incipient coating of lead upon the ferrous article may also be formed after the article has been freed from grease and scale as described in Example 1 by electrolysis of a bath of a solution of lead fluosilicate containing some free fluosilicic acid, a solution such as is customarily employed in electrol tic refining of lead being suit-- able for t e pur ose. The ferrous article having been'free from rease and scale is either immediately trans erred to the lead fiuosilicate solution or kept in Water so as to prevent oxidation during any appreciable interval before its transfer thereto. While in the lead fluosilicate bath the article acts as a cathode and electrolysis of the solution is effected by passing to the article, preferably from a lead anode, a direct current of low density for a very short time as, for example, a current of 12 amperes per sq. ft. of article surface for a period of from 15 to 45 seconds. This results in the formation on the article of a very thin coating of metallic lead which therefore differs in characteristics from the coatings produced as heretofore described, it being coherent as distinguished from spongy. After the formation of this coherent coating the article is removed from the bath, thoroughly Washed and then vigorously brushed with a steel Wire brush or like implement so as to remove the major or excess part of the lead coating and cause a considerable portion of the balance to penetrate into the pores of the surface of the article, thus, as in the other examples, producing a lead-ferrous surface for the subsequent reception of the zinc which may then be` plated thereon as in the foregoing examples.`

Numerous and comprehensive tests have shown that our improved zinc coated or plated ferrous articles display substantially one hundred fifty times greater resistance to corrosion than similar ferrous articles coated with the same amount of zinc by either the hot dipping or usual electroplating methods in which alkaline -cyanide solutions or neutral or substantially neutral zinc sulfate solutions are employed or, in other words, the zinc plated ferrous articles of our invention will under conditions and with equal thicknesses of zinc plating retain they latter in the presence of Weak acids some one hundred fifty times longer than similar ferrous articles plated with alike amount of zinc by electroplating or hot dipping in the usual Way. They also exhibit reater corrosion* resistant properties than similar ferrous articles having zinc coatings applied directly to their clean ferrous surfaces by electrolysis of high acid zinc sulfate solutions by high density currents delivered from insoluble anodes in accordance with the method disclosed in our said application Serial No. 305,429 but not, of course, to so great a degree since such articles have, among other things, markedly improved corrosion-resistant properties to those produced commercially by hot dipping or the usual electroplating processes' to which we have just referred. It should be noted that irrespective of the articular manner in which the incipient ead coating ma be initially formed upon the ferrous artic e the said coating is so subscquentl mechanically treated, as by brushing wit a steel brush, that a very large portion thereof is entirely removed and at least a considerable portion of the balance forced into the pores of the surface of the ferrous base so that a compound surface of lead and steel or iron, more o r less pervious and interrupted, is presented for the reception of the zinc in contradistinction to a continuous, impervious unbroken surface of either metal which would therefore in itself form a base for the reception of any subsequent coating or plating.

In the accompanying drawing which is designed to illustrate the progressive formation of the zinc plated ferrous article herein disclosed, Fig. 1 is a fragmentary cross section of the ferrous base B-as it appears when magnified approximately 200 diameters after it hasbeen pickled, cleaned and otherwise conditioned for the reception of the lead; Fig. 2 isa similar section after the application of the lead coating L; Fig. 3 is a similar section after the brushing operation whereby the excess of lead is removed and the remainder L forced into the pores and/or minute depressions in the surface of the base preparatory to the application of the zinc, and Fig. 4 is a fragmentary section through the finished article after the zinc plating Z has been applied. It will be observed from these several views that the surface s of the ferrous base exhibits a distinctly irregular contour When viewed under suitable magnification, and that, after the removal of the excess lead, the residual portion thereof is principally disposed, as shown in Fig. 3, in the depressions and/or pores of the base, while the pinnacles or proliections of the said surface are substantially free of lead whereby during the final zinc plating operation the zinc can attach itself directly thereto.

Thus, as shown in Fig. 4 of the drawing an article produced in Jaccordance with our invention may be considered as exhibiting three zones or strata, an inner stratum of ferrous material formed by the base B itself, then a thin stratum X in which ferrous material, lead and zinc are very intimately mixed, united and locked together, and then form com osition throughout; our invention, on t e other hand, neither contemplates, nor results in the production of, a mercurio or other alloy-zinc plating, but on the contrary and as distinguished therefrom, results in the production of a stratum or layer of substantially pure zinc upon a previously prepared surface of such character as to materially facilitate the deposit of the zinc lthereon yet without interfering with an intimate bonding of the latter with the ferrous base.

Having thus described our invention, We claim and desire to protect by Letters Patent of the United States:

1. As a new product of'manufacture, aferrous article having a plurality of irregularl shaped minute surface depressions, bodles of spongy lead disposed in and partially filling said depressions, and a coating of substantially pure zinc intimately associated with all of said bodies of lead and contacting said article itself inthe spaces between adjacent bodies.

2. As a newproduct of manufacture, a ferrous article having a plurality of minute spaced pointed surface projections, bodies of spongy lead disposed in the spaces between sald projections and intimately associated with the metal of the article and a coating of zinc overlying said projections and said bodies and presenting outwardly a continuous surface consisting of substanti-A ally pure zinc. v

3. As a new product of manufacture, a ferrous article having a coating of substantially pure zinc of appreciable thickness, the zinc contacting the metal of the article. at spaced points, and minute bodies of spongy lead interposed between the article and the coating and occupying the spaces between said points.

In Witness whereof We have afliXed our signatures.

SIDNEY H. DAVIS. CARL O. ANDERSON. WILLIAM N. SMITH. HERBERT R. HANLEY.

a third or outer stratum of substantially i pure metallic zinc Z. We are aware it has b een proposed to plate ferrous articles with z1nc by electrolysis of cyanide solutions containing mercury with a view to increasing the hydrogen overvoltage of the'article an facilitating the deposition of the zinc thereon; under such conditions, however,-the-fin v ished article ultimately produced exhibits a ferrous base having a coating or plating of a mercurio-zinc alloy ofl substantially uni- 

